The present invention relates to method and apparatus for sublimation transfer using a long, tunnel furnace.
Sublimation transfer requires pressing a sublimation transfer image against a surface while heating the surface and image to a temperature high enough to cause the sublimation transfer image to sublimate and transfer to the surface. One approach to achieve this sublimation transfer is to have pressing devices shaped to conform to the product shape press the sublimation transfer image against the product while heating the product and image. Arrangements for transferring images to a coffee mug are described U.S. Pat. No. 5,755,921 to Christensen and U.S. Pat. No. 5,944,931 to Cranford. These patents place the assembled pressing device, image and product in an oven and remove them after each sublimation transfer occurs. These one-at-a-time approaches are inefficient for handling large numbers of products because the time to load, unload, heat and cool each product is extensive and hence the accompanying cost is high. There is thus a need for an improved sublimation transfer process and apparatus.
Another approach to achieve this transfer is have sublimation transfer images held against the product surface by stretching elastomeric sheets to press the images against the product surface. The assembly is heated in a furnace, causing the images to transfer to the product surface under pressure provided by stretching the elastomeric sheets around the products to cause sufficient pressure for sublimation transfer. The elastomeric sheets and transfer process are as generally described in U.S. Pat. No. 8,002,931 to Wang et al. Sublimation transfer has used a mesh belt conveyor to move products along a long tunnel. These assemblies may be placed in the bottom of an oven or furnace, or they may be placed on an endless, moving conveyor belt that passes through a furnace to achieve the heating and sublimation transfer. But the wrapping of stretched material does not conform to the configuration of rapidly changing surfaces and each product is individually wrapped. This approach is thus inefficient for handling large numbers of products because the time to load, unload, heat and cool each product is extensive and hence the accompanying cost is high. There is thus a need for an improved sublimation transfer process and apparatus.
Vacuum has been used to draw flexible membranes against a surface in order to apply the pressure for sublimation transfer, with U.S. Pat. Nos. 6,814,831 and 7,810,583 describing such systems. But the vacuum systems use single trays that are immovable or reciprocate into or out of a heating chamber, limiting the use of the apparatus and quantities of resulting imaged products. There thus remains a need for an improved method and apparatus to efficiently apply sublimation images to products.